THIS invention relates to a spring pre-assembly for a mattress foundation unit.
A conventional mattress foundation unit, sometimes referred to as a xe2x80x9cbox springxe2x80x9d, generally includes a wooden base frame, spring modules and a mattress supporting wire grid that is supported above the wooden base frame by the spring modules. Whereas the spring modules are normally stapled to the wooden base frame below, various methods are used to secure the spring modules to the wire grid.
One method of securing the spring modules to the wire grid without the use of clips or welding is disclosed in U.S. Pat. No. 5,369,822, which is the use of downwardly extending and converging locking bars. Another method is disclosed in U.S. Pat. No. 5,197,155 and U.S. Pat. No. 5,142,716, wherein the top section of the spring module is being held in place by three grid wires extending over the top section and one grid wire extending under the top section.
Often, the wire grid and spring modules are manufactured and pre-assembled by a first manufacturer before being transported to a second manufacturer. The second manufacturer will typically complete the final mattress foundation unit by connecting the pre-assembly to the wooden base frame and applying the padding and covering. The ease of assembly and stackability of the pre-assembly are important design criteria for the first manufacturer.
According to a first aspect of the invention there is provided a spring pre-assembly for a mattress foundation unit having a rigid base, the spring pre-assembly including:
a plurality of spring units, each including a base portion, a pair of divergent, operatively upwardly extending leg portions and a pair of engagement portions extending at a generally horizontal attitude in opposite directions from operatively upper ends of the leg portions; and
an upper grid which includes a plurality of grid wire pairs arranged orthogonally to one another, each grid wire pair comprising a first grid wire and a second grid wire;
the base portions of the spring units being connectable to the rigid base and the engagement portions of the spring units being engageable with adjacent grid wire pairs of the upper grid, the arrangement being such that when the engagement portions are so engaged the spring units are pre-stressed.
Advantageously, the spring unit is formed from a single length of wire.
Ideally, each engagement portion includes two spaced apart straight wire sections, each straight wire section having a notch receiving the first grid wire and each straight wire section passing over the second grid wire, thereby to secure the engagement portion with the grid wire pair.
Preferably, each leg portion includes two spaced apart spring members. More preferably, each spring member has a U-shaped deformity therein. Most preferably, each spring member lies generally in a single plane and includes five straight wire sections extending between each engagement portion and the base portion and at least one bend between the straight wire sections.
Advantageously, the spring unit is symmetrical about an operatively vertical plane bisecting the base portion.
According to a second aspect of the invention there is provided a spring unit for a mattress foundation unit having a wire grid, a rigid base and a plurality of spring units extending between the wire grid and the rigid base, each spring unit including:
a base portion, a pair of leg portions divergently extending from the base portion and a pair of engagement portions extending in opposite directions from the distal ends of the leg portions;
the base portion being connectable to the rigid base;
the leg portions each having a U-shaped deformity; and
the engagement portions being generally co-planar with one another and each including a notch therein.
According to a third aspect of the invention there is provided a mattress foundation unit including:
a rigid base;
a plurality of spring units, each including a base portion, a pair of divergent, operatively upwardly extending leg portions and a pair of engagement portions extending at a generally horizontal attitude in opposite directions from operatively upper ends of the leg portions; and
an upper grid which includes a plurality of grid wire pairs arranged orthogonally to one another, each grid wire pair comprising a first grid wire and a second grid wire;
the base portions of the spring units being connectable to the rigid base and the engagement portions of the spring units being engageable with adjacent grid wire pairs of the upper grid, the arrangement being such that when the engagement portions are so engaged the spring units are pre-stressed.